In recent years, there are demands that display devices have a higher definition, a larger screen, and a flat dimension, and various types of display devices have been developed. Among those, gas discharge panels such as plasma display panels (hereafter referred to as “PDP”s) are receiving attentions as typical display devices.
In a PDP, a front panel and a back panel are disposed so as to oppose each other with barrier ribs interposed therebetween. The perimeter areas of the panels are sealed together so as to form a space (discharge space) between the panels, and discharge gas (for example, a Ne—Xe gas mixture of 53.2 kPa to 79.8 kPa) is sealed in the space. The front panel has a front glass substrate, a pair of display electrodes that are provided in stripes on the surface of the front glass substrate, a dielectric glass layer covering them, and a dielectric protection layer (MgO) that further covers the dielectric glass layer.
The back panel has a back glass substrate, a plurality of address electrodes that are provided in stripes on the surface of the back glass substrate, a dielectric glass layer covering them, and barrier ribs that are disposed on the dielectric glass layer so that each of them stands between two address electrodes. Further, on the back panel, phosphor layers for red (R), green (G), and blue (B) are disposed on the walls of the grooves each defined by adjacent barrier ribs and the dielectric glass layer. As examples of phosphor members included in the phosphor layers, generally speaking, Y2O3:Eu is used for red, Zn2SiO4:Mn is used for green, and BaMgAl10O17:Eu2+ is used for blue. Especially, as the phosphor member for green, a substance that contains Si (silicon) in its composition is sometimes used in order to improve the luminance of the panel when the panel is driven.
In principle, the PDP described above is driven using a method (called the intrafield time-division grayscale display method) in which binary values for turning the light on and off are used, and for each color, one field is divided into a plurality of sub-fields so that a lighting period is subject to a time division, and different levels of gray are expressed with combinations of the sub-fields. An image is displayed on the panel using the ADS (Address Display-Period Separation) method according to which, in each sub-field, a series of operations is performed, which is to perform writing in a discharge cell to turn the light on during an address period and to maintain the discharge during a sustain period that follows the address period.
As described above, when a light emission drive of a PDP is performed, in order to display an image, wall charges are generated on the surface of the dielectric protection layer in selected discharge cells during an address period, and discharges occur during a sustain period. The amount of the wall charges being accumulated is influenced by the impedance of the dielectric protection layer; therefore, when the impedance of the dielectric protection layer is too much lower or too much higher than a predetermined value, what is called “black noise” may occur, which means that discharges during the sustain period do not occur in a normal manner. Further, when the impedance is too high, in order to have discharges occur during a sustain period, it is required to apply a high voltage, and thereby the consumption electric power becomes large.
A technique has been developed to make the impedance of a dielectric protection layer at a desired level so that the electron release characteristics of the dielectric protection layer are optimized, by adding, to the dielectric protection layer, a Group IV element such as Si, or a transition metal such as manganese (Mn) and nickel (Ni), or an alkali metal, or an alkaline earth metal (The Unexamined Japanese Patent Application Publication No. 10-334809).
However, a PDP sometimes experiences a problem that in some of the discharges cells, the impedance of the dielectric protection layer gradually changes from the initial set value as the PDP goes through its driving period. When the impedance of the dielectric protection layer changes as the PDP goes through its driving period, after the PDP is driven for a long period of time, what is called “black noise” will occur, which means that no discharge is generated during the sustain period in a discharge cell in which the light is supposed to be turned on. This phenomenon similarly occurs even in a case where, like the PDP disclosed in the publication cited above, Si is added to the dielectric protection layer during the manufacturing process.